The present invention relates generally to gas meter calibration equipment, and more particularly to a device for testing a gas meter temperature compensator.
To create and maintain a fair and efficient marketplace for the buying and selling of natural gas and most dry clean gases, government agencies routinely conduct verification testing to ensure that gas meters are capable of accurate measurement and to prevent gas meters of inferior quality from entering the marketplace. The approval process requires that gas meters undergo comprehensive testing throughout their measuring ranges and at conditions which simulate the environment in which they are intended to operate. Due to large energy consumptions, the negative impact of an unacceptable gas meter measurement error is high.
In gas meters, particularly those for industrial use are required to measure large volumes of gas for heating or cooling purposes. It is necessary to allow for density changes in the gas being metered, particularly for temperature fluctuations. As the temperature rises and the volume of gas increases, the heating capacity of a given volume of gas is reduced. Since most gases are normally sold to the industrial user on the basis of a price per volume at standard temperatures, which is equivalent to a price per thermal unit of heating capacity of the gas, suitable allowance for temperature fluctuations in the gas volume measuring device should be made.
This can be conveniently accomplished by coupling a temperature compensator to the gas meter upon which the consumer records the volume of gas consumed for automatic temperature compensation. U.S. Pat. No. 3,969,939 to Grzeslo discloses an example temperature compensator that uses a temperature sensing element which contacts the flow of gas being metered. Gas flowing through the associated gas meter causes rotation of the impellers of the gas meter which drives a shaft that acts as a driving element which initially converts the dynamic movement of the impellers to an uncorrected volume of gas flow. Also, the temperature sensing element adjusts the position of a cam which affects the travel of a cam striker element to provide temperature correction within the device.
Typically, it is necessary to conduct periodical calibration testing of temperature compensators, in order to ensure accurate operation over the lifetime of the device. Due to the appreciable cost of a undetected measurement error, temperature compensators must be carefully tested. Specifically, the temperature sensing elements of temperature compensators are subjected to predetermined temperature test points, each with an extremely small margin of error. Accordingly, it is necessary to utilize testing equipment which can provide certain temperature test points with a high degree of stability and accuracy.
One conventional temperature compensator testing device uses refrigerated and heated antifreeze baths to provide the necessary temperature test points. This testing device typically requires the temperature sensing elements (and accordingly the temperature compensator) to be positioned in a vertical static orientation. Since temperature compensating devices are conventionally positioned horizontally during operation, generated test results may not reflect true operating conditions. In fact, Canadian government compliance testing protocols currently demand either horizontal or vertical dynamic testing which is difficult to comply with using this type of testing method. Since this method requires the installation of two or three liquid calibration baths, as well as supporting electrical and hardware parts (e.g. refrigerant/heater portions and motor drive), the testing device is relatively expensive, cumbersome, complicated in design and requires a significant amount of electricity for operation. Due to the poisonous nature of the test fluid and high operational power requirements, this method is also environmentally detrimental. The liquid calibration baths require frequent calibration and are generally not able to provide accurate temperature settings (e.g. typically xc2x10.1xc2x0 F. changes throughout the liquid baths) or rapid temperature stability.
Another conventional testing device uses an environment gas chamber with associated circulating fans, duct work and mechanical drive system. While this device provides for horizontal testing, it also has several significant disadvantages. First, due to its cumbersome components, it is relatively expensive, heavy, cumbersome and complicated in design and requires large amounts of energy for operation. This device is not capable of maintaining accurate temperatures (e.g. xc2x10.1 xc2x0 F. changes throughout the system) and it is difficult to obtain rapid temperature stability. Finally, the compressors and refrigerant levels must be frequently monitored, maintained and calibrated for proper operation. Finally, moisture problems tend to develop within the system due to the entry of unfiltered air.
Accordingly, there is a need for an improved gas meter calibration device which provides accurate, rapid and stable temperature test points, which allows for the temperature compensator to be tested in its natural horizontal position, which is simple to operate, environmentally clean and which is compact, light in weight, durable and relatively inexpensive to manufacture.
The present invention provides a gas meter calibration testing device for providing first and second temperature test points for testing a fluid flow meter temperature compensator having a temperature sensitive element and a driving shaft wherein said temperature sensitive element is sequentially subjected to said first and second temperature test points, said testing device comprising:
(a) a vortex cooling tube having an input port for receiving compressed gas, a cold gas port for dispensing a cold gas stream and a hot gas port for dispensing a hot gas stream;
(b) a cold gas chamber coupled to said cold gas port, said cold gas chamber having a body and an insulative layer disposed along a substantial portion of said body to maintain the temperature of the cold gas stream substantially constant within said cold gas chamber such that said cold gas chamber provides the first temperature test point; and
(c) a hot gas chamber coupled to said hot gas port, said hot gas chamber having a body and an insulative layer disposed along a substantial portion of said body to maintain the temperature of the hot gas stream substantially constant within said hot gas chamber such that said hot gas chamber provides the second temperature test point.
The present invention also provides a method of calibrating a fluid flow meter temperature compensator of a gas meter, said method comprising the steps of:
(a) supplying a stream of compressed gas to a vortex cooling tube to generate a cold gas stream and a hot gas stream;
(b) maintaining the cold gas stream at a substantially stable first temperature test point for the temperature compensator;
(c) subjecting the temperature compensator to the first temperature test point;
(d) maintaining the hot gas stream at a substantially stable second temperature test point for the temperature compensator;
(e) subjecting the temperature compensator to the second temperature test point; and
(f) monitoring the temperature compensation provided by the temperature compensator during steps (c) and (e).
The above amendments are intended to bring the xe2x80x9cSummary of the Inventionxe2x80x9d into line with the claims, as amended. It is submitted that the amendments are fully supported by the application as filed, and that no new subject matter is being introduced.